You can use FBReader to read .chm files. It works ok if the files are not too big.

Ok, I don't think CHM support will be necessary then.

And as promised, now that the 2.0 source code is available, here's a preview of the zip browser. It should work on both the DR800S(G) and DR1000, with the 2.0 firmware. Installing associates .web and .zip files with the program. Keep in mind that zipbrowser looks for a file called index.html or index.htm in the root directory of the zip file. You can zip complete websites with multiple html files, images and other resources.

MAFF/maf files are not supported yet, but I plan to add support in the future (it requires parsing some rdf files).